Enhancing Stability and Efficiency of Perovskite Solar Cells with a Bilayer Hole Transporting Layer of Nickel Phthalocyanine and Poly(3‐Hexylthiophene)

Abstract

To expedite the commercialization of perovskite solar cells (PSCs), researchers are exploring the feasibility of employing nickel phthalocyanine (NiPc) as a hole transport material (HTM) due to its cost‐effectiveness, excellent thermal stability, and suitability for solution coating. However, the low LUMO energy level of the NiPc may limit its ability to block photoelectrons generated in the perovskite layer from recombining with holes, which can reduce the overall efficiency of the solar cell. One solution is to use cascaded bilayers with HTMs that have relatively higher LUMO levels. In this study, a bilayer consisting of NiPc and poly(3‐hexylthiophene) (P3HT) is employed as the HTM, where the P3HT exhibits vertical phase separation during the coating process. By optimizing the mixing amount of P3HT into the NiPc, a record power conversion efficiency of 23.11%, the highest reported for NiPc‐based PSCs is achieved. Moreover, an excellent long‐term stability is demonstrated by encapsulating the PSC in polyisobutylene, with the device retaining 90% of its initial efficiency after exposure to 85 °C and 85% relative humidity for 1000 h.

Recent Advances in Poly(3‐hexylthiophene) and Its Applications in Perovskite Solar Cells

“…[98] Kim et al introduced a bilayer HTL consisting of NiPc and P3HT, where a vertical phase separation occurred after optimization leading to a binary formation and achieving a high efficiency of 23.11% PCE. [33] The vertical separation promoted the charge extraction and electron blocking properties of the device and improved the stability response when encapsulated in polyisobutylene, retaining 90% of its initial efficiency after exposure to 85 °C and 85% relative humidity for 1000 h. [33] In a remarkable study, Jeong et al reported the incorporation of gallium (III) acetylacetonate Ga(acac) 3 into P3HT HTL (Figure 3). [32] Ga(acac) 3 interacts with the perovskite surface, passivating the defects on the perovskite surface and reducing the interfacial trap-assisted recombination loss.…”

“…As shown in Figure 9, the P3HT-based PSCs have shown a relatively stabilized performance, especially in the last years of the progress. [30][31][32] Compared to lithium-doped Spiro-OMeTAD PSCs, P3HT-based devices not only achieved higher efficiencies >23% PCEs compared to Spiro-based PSCs (≈21% PCEs), [30][31][32][33] but also showed a better tolerance to withstand harsh conditions and continuous illumination at MPP. [27][28][29] At the same conditions, Spiro-based devices show a very sharp decline in their efficiencies, whereas the perovskite layer underneath is observed to undergo clear degradation, yielding many impurity peaks shown by X-ray diffraction (XRD) measurements.…”

“…Compared to other organic hole-transport material (HTMs), Spiro-OMeTAD is used in high concentrations (>70 mg ml À1 according to different researchers), [27][28][29] which is about one-seventh that of other organic HTMs. [30][31][32][33][34] Despite the relatively comparable costs of the batches of each compound, the Spiro-based PSC devices are considered more expensive according to cost-per-unit scales. [35] Various classes of materials have been developed and used as HTMs for PSCs, including small molecules, π-conjugated polymers, organometallic compounds, and metal oxides.…”

“…[39,40] Also, P3HT has advanced thermal and moisture stability making P3HT-based PSCs highly resistant to environmental stress. [31][32][33] Furthermore, simple processing and low cost are very significant to large-scale production making P3HT one of the best HTM candidates for large-area PSC devices and modules. [40][41][42] The first PCE reported of P3HT-based PSCs was only 0.52% combined with MAPbBr 3 active layer.…”

Correlating Carrier Dynamics with Performance in Perovskite Solar Cells

“…[10] Currently, effective methods to improve the efficiency of PSCs involve advanced structural and material design, combined with high-quality passivation at perovskite-related interfaces and grain boundaries. [11][12][13][14][15][16][17][18] For instance, Xu et al introduced an insulator alumina nanoplate with random nanoscale openings between the perovskite absorber and transport layer to reduce contact area and minimize surface recombination. [19] This led to a high efficiency of 25.5% with remarkable open-circuit voltage (V OC , 1.208 V) and fill factor (FF, 84.37%) for a p-i-n PSC.…”